Maintaining a safe environment in deep-pit swine production facilities is a primary goal, and one that takes time and consideration. One risk that can increase when the buildings are closed up and heaters kick on is methane production. Last fall, some producers learned first hand that the risk can lead to disaster.
Methane production in deep-pit storage facilities is unavoidable and, if not managed carefully, can cause a fire. As foam develops in the pit, it becomes more dangerous and increases the risk.
“To our knowledge there were eight fires in Iowa that occurred in deep-pit facilities in the fall of 2009; it’s possible that more occurred,” says Robert Burns, agricultural and biosystems engineer at Iowa State University. Looking for common denominators, Burns has investigated five of the eight fires.
There also were reports in southern Minnesota and a few other spots.
“Fires resulting from methane produced in deep-pit swine facilities can result in varying amounts of damage,” Burns notes. “Flash fires can race through the barn causing significant damage but leaving the structure intact.” However, other fires can destroy the entire facility.
Fires can result if ventilation is inadequate and methane is present in 5 percent to 15 percent concentrations. “Methane is obviously a fuel and, if present in this concentration, can explode if there’s an ignition source,” Burns warns.
Hydrogen sulfide and phosphine gas, if present in adequate concentrations, also can present a risk. “We don’t believe, however, that hydrogen sulfide or phosphine are resulting in the fires,” Burns adds. “We believe methane is fueling the fires.”
Foam production in deep-pit manure systems is a complicating factor in some facilities. Attempts at breaking up the foam may exacerbate the problem because the foam is full of gas bubbles composed mostly of methane and carbon dioxide. These gases are created from manure’s slow decomposition in the pit.
The foam captures and holds methane and may contain from 50 percent to 75 percent of the flammable gas. “When you break up that foam and the air mixes upward into the housing area, the methane can be diluted down to the explosive limits,” Burns warns. If an ignition source is present, such as a heater, a flash fire may occur.
While not a new phenomenon, foaming seems to be occurring more often and affecting more operations. “We believe there is a link between foaming and the explosions,” says Larry Jacobson, agricultural and biosystems engineer at the University of Minnesota.
Foaming by itself is a problem because it reduces pit volume and is unwieldy to pump. “If the pit foam comes up through the slats, it, of course, gets on the pigs and can get ugly,” Jacobson says.
Of the five swine facility fires that Burns investigated, all had foam present in the manure pit. Unfortunately, foam production in deep-pit manure systems is not fully understood at this time.
In four cases, Burns found that barn heaters were identified as ignition sources, and methane was the main fuel.
Spraying or sprinkling water or agitating the pit can help reduce foam build up. However, special precautions are necessary to prevent explosions or fires. (See accompanying sidebar.)
Proper ventilation is critical in these instances. As a result of foam build-up, pit-fan effectiveness may be reduced, making more ventilation necessary via the wall fans.
“In a mechanically ventilated barn, it’s usually best to rely on properly operating air inlets and avoid opening the barn up too much because you lose static pressure,” Jacobson says. “On curtain-sided buildings where only pit fans are present, they will have to be employed. In those cases, be sure that curtains are open.”
The bottom line is to be cautious when attempting to break down foam in deep-pit storage facilities. Jacobson advises providing at least four air changes per hour during the agitation process. However, it may be necessary to ventilate at up to 10 air changes per hour, he adds. “Agitation should be avoided until the manure level is 2 feet below the slats.”
There are no known agents that are reliable in preventing foaming. “I would be surprised if there is a silver bullet that is found to prevent foam,” Jacobson says.
Defoaming agents or surfactants may be useful but have not been consistently reliable, according to Jacobson. “If used, surfactants may work in one building but not in another,” he says. “They should be tested in a limited area before widespread use.”
Researchers also have not seen any consistent patterns among operations using the same genetics, feed or other production regimens. Consequently, they are digging into the data and planning research to find out more.
Until more details are known about the cause of foam formation in deep-pit manure storage and the resulting fire risk, caution is the best course. Being aware is an important first step.
Foam Requires Caution
While foam development in manure pits is not fully understood, many researchers are looking into the problem and searching for answers. Until then, Ted Funk, agricultural engineer, University of Illinois Extension, provides the following guidelines to help minimize risk if you face a foam challenge.
Before attempting to break down the foam, review emergency action plans and make sure all workers have ready access to emergency contact information.
Fully open all ventilation curtains or ventilation pivot-doors and operate ventilation fans at maximum speed.
Prior to agitating or pumping the pit, turn off electrical power to any non-ventilation equipment; extinguish pilot lights on heaters or other potential ignition sources within the building.
If foam is present in liquid-manure pits, agitate slowly and cautiously.
Make sure all workers are out of the building and clearly tag all entrances, noting that the building is unsafe for entry during agitation and pumping.
Always begin the agitation process slowly and increase speed over time. Agitate the manure keeping the jet of pressurized manure below the liquid surface to avoid “rooster-tailing.” Don't let the jet of manure strike walls or columns within the pit.
Continue maximum ventilation for 30 minutes after pumping has ended before anyone re-enters the building.
"While we are not sure exactly what has led to last fall’s problems, we think these practices will help minimize accidents," Funk says.